Anyone else struggled fitting a 100Ah lithium under the bed in a Transit base?

Right so this is going to sound incredibly stupid but hear me out.

I spent an entire Saturday convinced I could just sort of... angle the Fogstar 100Ah in sideways and it would magically slot into the frame I'd built. It did not. What it did instead was get wedged at about 47 degrees while I was underneath the bed on my back, arms fully extended, slowly losing the will to live.

The Transit bed base is a proper awkward shape isn't it? That wheel arch cuts into everything. I ended up having to rebuild the whole wooden frame about three times before I got the clearances right. By the end I was essentially a man made entirely of sawdust and regret.

What actually worked for me:

• Measuring the actual usable cavity (not the "looks about right" cavity — learned that one the hard way)
• Building the battery box first, then fitting it as a unit rather than trying to drop the battery in afterwards
• Leaving more cable run than you think you need for the Victron SmartShunt connections

The battery is now beautifully installed and I'm very proud of it. My partner has pointed out that nobody will ever see it. She's right but she doesn't understand.

Anyone else gone through this particular circle of hell? And has anyone managed a second 100Ah in there without absolutely butchering the storage space? I'm tempted but the bed frame is already looking at me with what I can only describe as suspicion.

@DriftWizard not stupid at all — I did exactly the same thing with my cabin build, convinced myself a 105Ah would fit in a compartment that was clearly 2cm too short. Spent an embarrassing amount of time with a tape measure "double-checking" the same measurement hoping it would change 😅

Few things worth knowing with Fogstar specifically — they're pretty chunky compared to some rivals. Worth looking at the Fogstar Drift slim profile versions if space is genuinely tight.

Also, can you mount it vertically? Most lithium (LiFePO4 anyway) are fine on their side unlike old lead-acid. Just check your specific model's datasheet first.

What are your actual compartment dimensions? Someone here will have solved it already.

Had the exact same drama with my setup mate. Spent ages convinced I could squeeze a battery in somewhere it physically couldn't go — turns out foam insulation adds about 25-30mm you never account for when measuring.

What sorted me was doing a full cardboard template of the space first, then comparing to the actual battery dimensions. Sounds daft but saved me a second wasted trip to the van.

Worth checking whether you actually need 100Ah in one unit — two Fogstar 50Ah slim units stacked or split might give you more flexibility depending on your void shape. That's what @EmmaEdwards82 probably found with cabin builds too, awkward spaces rarely match standard battery footprints.

Also double-check your Transit year, the under-bed void dimensions changed between generations.

@DriftWizard the "it'll definitely fit if I tilt it just right" phase is practically a rite of passage 😄

Worth knowing: the Fogstar 100Ah is actually quite generously sized compared to some alternatives. If you're truly tight on space, the Fogstar Drift 100Ah slim form factor is worth a look — noticeably shorter height, which transforms what's possible under Transit beds.

That said, before you start shuffling batteries about again, grab a cardboard template of the exact dimensions and test-fit that first. Sounds daft but it saved me an absolute nightmare when I was configuring my setup.

Also check whether you're fighting the battery or the cabling routes — sometimes it's actually the Victron SmartShunt or terminal clearance eating your space rather than the cell itself.

Has anyone tried going upright in that space instead? On my narrowboat I had a similar headache with a tight locker — ended up standing the Fogstar vertically and it actually cleared things nicely, though I did double-check with Fogstar that orientation wasn't an issue for that particular cell chemistry (it wasn't).

Might be worth measuring the height clearance under the bed frame before committing — Transit bases can vary quite a bit depending on year and whether there's a crossmember in the way. What exact dimensions are you working with? Sometimes the answer is a slimmer 100Ah rather than fighting the one you've got.

@MultiPlus_Queen upright mounting is fine with LiFePO4, unlike old lead acid. No acid to slosh about.

Done exactly this in my Transit motorhome — stood the Fogstar on its end in a narrow side locker that had no business fitting a battery. Works perfectly.

Measure twice though. Then measure again. Then accept it still won't fit and order the slimline version anyway. 😄

Only thing to check is your BMS doesn't get wedged against anything metal — learned that one the hard way when a vibration rattle turned out to be terminal covers slowly working loose against the chassis.